Prior art solar collector structures of the type with which the present invention might be compared may be categorised generally as falling within two groups; a first group that employs effectively a single absorber tube that extends along the focal line of a non-inverted trough-type reflector and a second group that employs a single absorber tube that extends along the focal line of an inverted trough-type reflector. Collector systems of the first group suffer the disadvantages that the absorber tube collects incident solar energy from one only reflector element and requires complex mounting and fluid coupling arrangements. Collector systems of the second group largely avoid the disadvantages of the first group but suffer the disadvantage of losses occasioned by the need for multiple reflections, firstly from ground-mounted reflectors and then from the inverted trough reflectors. Moreover, collector systems of the second group (if not both groups) suffer a relatively high emissivity-to-absorptance ratio as a consequence, in part, of the surface area-to-aperture ratio attributable to the relatively large diameter tube required of a single-tube collector system. Furthermore, as a secondary issue, collector systems of both the first and second groups suffer loss of operating efficiency due to movement of unconfined heated air from the interior of the trough-like reflectors. Still further, as a tertiary issue, to the extent that the collector systems of the first and second groups employ a single absorber tube, those collector systems are not capable of providing for a variable absorption aperture.